1. Field of the Disclosure
The present disclosure relates to a control apparatus for a hybrid vehicle including an internal combustion engine, an electric motor and a storage battery that supplies electric power to the electric motor.
2. Description of Related Art
Conventionally, a hybrid vehicle (hereinafter, also simply referred to as vehicle) travels while controlling an electric motor and an internal combustion engine such that the capacity of a chargeable and dischargeable storage battery is efficiently utilized for the purpose of improvement in the fuel consumption performance of the vehicle.
On the other hand, it is known that a repetitive change in an extremely large remaining amount of charge (hereinafter, also simply referred to as state of charge (SOC)) or extremely small remaining amount of charge of the storage battery accelerates the performance degradation of the storage battery. Therefore, the SOC of the storage battery is managed for the purpose of preventing the degradation of the storage battery. Specifically, the upper limit and lower limit of the SOC are prescribed, and a control apparatus manages the SOC such that the SOC does not go beyond the range (referred to as management range) between the upper limit and the lower limit.
That is, the control apparatus prohibits charging the storage battery when the SOC reaches the upper limit. At this time, electric energy that is generated as a result of regenerative braking is transformed into thermal energy in a friction brake device or an inverter or both, or the like, so energy originally recoverable and usable for propelling the vehicle is consumed uselessly. In contrast, when the SOC reaches the lower limit, the control apparatus forcibly charges the storage battery by using the output power of the internal combustion engine. As a result, fuel is consumed due to a cause other than propelling the vehicle. Therefore, causing the SOC not to reach the upper limit or the lower limit during traveling of the vehicle leads to effective improvement in the fuel consumption performance of the vehicle.
When the vehicle travels on such a downhill that the vehicle accelerates without using the torque (driving force) of the internal combustion engine or the electric motor, braking force is required from the vehicle when a driver releases the foot from an accelerator pedal or possibly further depresses a brake pedal. At this time, an increase in vehicle speed is reduced or prevented by the regenerative braking force of the electric motor, and electric power generated as a result of regenerative braking is supplied to the storage battery. As a result, the SOC of the storage battery increases.
Therefore, when the vehicle travels on a long downhill (that is, a section having a relatively long distance and a relatively large altitude difference), the SOC may reach the upper limit halfway on the downhill, and the SOC cannot be increased any more. This means that the effect of improvement in fuel consumption, which is obtained as a result of traveling on a downhill, increases as the difference between the upper limit of the SOC and the SOC at the start point of the downhill increases.
One of existing control apparatuses for a vehicle (hereinafter, referred to as existing apparatus) acquires the position of the vehicle, a destination, road information, and the like, with the use of a navigation system, and determines a scheduled travel route and a downhill section in the scheduled travel route on the basis of those pieces of information. The existing apparatus estimates the amount of electric power that is newly chargeable into the storage battery through regenerative braking in a period during which the vehicle travels on the determined downhill section. When the estimated amount of chargeable electric power is larger than an ordinary management range, the existing apparatus expands the management range of the storage battery to an expanded management range. In addition, the existing apparatus controls the electric motor or the internal combustion engine or both such that the SOC of the storage battery is consumed to the lower limit of the expanded management range by the time the vehicle starts traveling on the downhill section (see, for example, Japanese Patent Application Publication No. 2005-160269 (JP 2005-160269 A)). Hereinafter, such control is referred to as specific control, and a section on which specific control is executed is referred to as controlled target section.
However, usually, the road information that is acquired by the navigation system is periodically updated. For example, vehicle information communication system (VICS) (registered trademark) information that is one of such pieces of information is updated every five minutes. Therefore, if the road information is updated when the vehicle is in the middle of traveling on a downhill that is a controlled target section while executing specific control, and then a target downhill section is redetermined on the basis of the road information, the existing apparatus may not be able to determine the remaining part of the downhill on which the vehicle is traveling at that point in time (the part of the downhill on which the vehicle will travel thereafter) as a downhill section on which specific control should be executed because the distance and/or altitude difference of the remaining part is small. In this case, the existing apparatus stops specific control, so there is a concern that the effect of improvement in fuel consumption reduces.